Field of the Invention
The present invention relates to a method of handling an end portion of a continuous sheet, rolled in the form of a paper roll, when a printing operation is performed on the continuous sheet.
Description of the Related Art
In a printing apparatus that prints on roll paper, a continuous sheet of the roll is unwound from an outermost periphery and moved under a print head for image printing. This type of printing apparatus cuts the continuous sheet according to the size of a printed image and discharges the printed cut sheet onto a tray. A tail end portion of the paper roll often requires special processing for the following reasons. First, it is necessary to prevent one complete image from being broken halfway by the tail end of the roll. Second, even if the image has been printed completely to the end, too short a distance from the cutting position to the tail end of the roll can result in the remaining unprinted sheet failing to be conveyed in the printing apparatus in either direction, forward or backward. To minimize a wasteful use of the roll paper while at the same time keeping the last non-printed cut sheet large enough to be able to be conveyed in the printing apparatus, it is therefore required to detect and manage the tail end of the roll correctly for its smooth conveyance.
Japanese Patent Laid-Open No. 2001-171881, for example, discloses a construction in which a unit is provided to measure the diameter of a paper roll to manage the distance that a continuous sheet of the roll is fed from when the roll diameter has reduced to a threshold value. More precisely, this method involves presetting as a maximum available length the distance that the continuous sheet of the roll can be fed from when the roll diameter has reduced to the threshold value and stopping printing when the distance that the continuous sheet has been fed after the roll diameter decreased to the threshold value has reached the preset maximum available length. With the technique of Japanese Patent Laid-Open No. 2001-171881, it is possible to avoid a remaining unprinted sheet, which has been cut and separated from the printed sheet, becoming unable to be conveyed, while at the same time minimizing a wasteful use of the paper roll.
In Japanese Patent Laid-Open No. 2001-171881, however, a comparison is made between the maximum available length and the distance the continuous sheet has been fed (accumulated length) each time one line is printed. When the accumulated feeding length has reached the maximum available length, the printing of the next line is stopped. So, when an image extending over a plurality of lines is printed, there is a possibility of this image being broken partway near the tail end of the roll. Furthermore, Japanese Patent Laid-Open No. 2001-171881 does not give a detailed description of how, after the printing operation has been stopped, the printed sheet and the unprinted sheet separated by cutting are discharged. Since the printed and unprinted sheets are discharged en masse, the user is left with the task of sorting them out.